1. Field of Invention
This invention relates generally to use of hand tools for conducting rotary operations, particularly to the use of such hand tools where axial alignment of the tool to the intended target is important to the success or the quality of the operation.
More particularly, this invention relates to the manually conducted rotary cutting of threads in work pieces to provide a mating component to threaded fasteners such as bolts, and for other extended purposes where such features are useful.
Even more particularly, this invention relates to use of such hand tools in a machine shop environment where work pieces may be subjected to other operations requiring rotary-operated machinery such as drill presses and lathes.
Most particularly, this invention relates to means of adapting such hand tools to use mechanical support to aid in maintaining axial alignment of the hand tool to the intended target during thread-cutting or other rotary operations on a work piece secured in a lathe or drill press or other rotary machine, without detracting from the benefits of manual control of rotational and longitudinal force and motion during such operations.
2. Description of Prior Art
Often a machinist is called upon to tap a drilled hole in a work piece already secured in, for example, a lathe. It is essential that the tap be held in careful, close axial alignment with the center line of the hole in the work piece, to prevent breakage of the tap, possible injury to the machinist, irreparable damage to the work piece, and to provide strong, true threads which will readily accept and secure a mating member.
A hand-held tapping operation as has normally been practiced is time consuming in the setting up of the work piece for drilling, and then removing the work piece to another position where it must again be set up for tapping, and perhaps then returned to the original station for further operations. Furthermore, the hand-held tapping operation does not ensure a perfectly aligned tap in relation to the work piece, so that the use of the hand held tap requires a skilled and experienced operator to properly perform the tapping operation. Manual tapping does, however, offer the important benefit of manual dexterity and sensitivity to varying longitudinal and rotational resistance inherent with different tap sizes and different materials.
The solution to the axial alignment problem of simple, unaided, hand tapping of threads is to employ mechanical means for axial support. Fully automated machinery is available for high volume work which includes tapping operations, but such machines are expensive and generally entail significant set up time.
For custom, low volume and pre-production applications, there are three generally accepted ways for employing mechanical means to aid in the manual tapping process: 1.) Insert the proper tap into the tail stock drill chuck of a lathe and turn the head stock and work piece by hand onto the tap, 2.) Follow the tap and tap handle into the work piece with the tail stock live or dead center, or 3.) Center a pulley tap in the center-rest while turning the tap by hand with a thin open-faced tap handle.
Similar tapping methods are used with other rotary-operated machines such as a drill press or milling machine. None of these methods are particularly easy, and all require accessory devices and are time-consuming and troublesome.
Efforts to shorten tapping time and eliminate misalignment and tap breakage have resulted in relatively complicated and expensive accessory tools, special tap holding chucks and turning wheels engaging the chucks, and special tap holders. The following patents are illustrative of the prior art:
Proffitt U.S. Pat. No. 4,988,243, Jan. 29, 1991: A chuck-mounted, spring loaded, centering tip that can be latched in a retracted position and released to engage and push on the butt end of a conventional tap handle and tap. This is a relatively complicated and costly accessory that may subject the tap, workpiece, and initial threads to excessive longitudinal pressure in order to maintain the axial alignment and mechanical integrity of the setup. It has a long axial length which means the chuck mount may have to be moved well back for installation. The device does not provide any supplemental turning means to assist the operator in rotating the tap handle.
Park U.S. Pat. No. 4,856,946, Aug. 15, 1989: Uses a rachet for torque, has its own tap chuck to hold the tap, and uses a chuck-mounted "press member" with external pressure to maintain a longitudinal force through the centering guide of the rachet assembly to keep the assembly axially aligned while in use. A relatively complicated and costly accessory with a long axial length; the method requires the application of longitudinal pressure which may be excessive for many tap sizes and work piece materials, in order to maintain axial alignment and mechanical integrity of the setup. Also, it is not readily adaptable to be used with conventional hand-held tapping tools.
McCoy U.S. Pat. No. 4,687,384, Aug. 18, 1987: A hand-held tapping tool incorporating a spring-loaded slider and graduated scale between the handle and the tap chuck. The device is intended to be back-stopped by a chuck-mounted tip under pressure from the spring in the tap handle. The progress of the tap into the work can be measured by use of the scale on the tap handle. A relatively complicated and costly accessory, it is likewise dependent on exerting a longitudinal force on the chuck-mounted tip sufficient to maintain the axial alignment and mechanical integrity of the setup, without regard to the potentially detrimental effect of excessive longitudinal force on the tap, work piece and initial threads.
Wood U.S. Pat. No. 4,087,195, May 2, 1978: Similar to a conventional manual tap handle, but modified to fit into the chuck of a rotary-operated machine. The device has an axially slidable, rotatable support means on the butt end which can be chucked to provide axial support without longitudinal pressure. Unnecessarily duplicative of features of a conventional hand tap handle.
Johnson U.S. Pat. No. 3,364,510, Jan. 23, 1968: A slidable, rotatable, chuck-mounted tapping tool with a keyed tap chuck and an external collar and rachet handle that fits over external splines to provide turning torque. A relatively complicated and costly accessory.
None of these devices combine the full utility of the conventional tap handle which is a basic item in the tool box of every machinist, with a minimal accessory adaptor which provides mechanical axial support without introducing unnecessary longitudinal force and without impeding the natural feel of the hand tap operation.